Method and apparatus for audio signal processing

ABSTRACT

An audio signal processing method wherein it is detected whether the data supplied from an optical disk reproduction apparatus or the like has continuous zero data for a predetermined period of time, and in the case where zero data continue for the predetermined period of time, it is determined that compressed audio data is involved, and the supplied data is decoded.

TECHNICAL FIELD

The present invention relates to an audio signal processing method andan audio signal processing apparatus. In particular, this invention isapplicable to an audio signal processing apparatus for decoding audiodata, an audio signal processing method and an optical disk apparatus.

BACKGROUND ART

The digital data (IEC61937 format) output from a digital audio terminalof a DVD (digital versatile disk) reproduction apparatus includes, likein the conventional CD (compact disk), compressed audio data of variousformats such as AC-3 (trade mark) proposed by Dolby, MPEG and dts (trademark) proposed by DTS, in addition to the linear PCM (pulse codemodulation). An external decoder unit connected to the DVD reproductionapparatus, therefore, is required to determine these data formats andaccurately process the data.

These compressed audio data, as viewed from the decoder unit, are simplythe conventional 16-bit PCM data, and until the sync signal in the burstpreamble existing in the 16-bit data is detected, it cannot bedetermined whether the particular data are actually PCM data that can bedemodulated or the compressed audio data requiring the decode processingsuch as expansion processing.

This determination is possible to some degree for the DVD reproductionsignal by detecting the PCM flag or the channel status on the IEC61937format. The CD recorded in the dts format recently marketed in the U.S.,however, is handled as a normal CD (compact disk) also in the DVDreproduction apparatus, and therefore the PCM data is determinedaccording to the PCM flag with a risk.

In view of this, in the conventional decoder apparatus, the bit patternof input data is always compared with a conceivable sync pattern, andupon detection of any sync signal indicating compressed audio data, theaudio decoding of the PCM data is suspended, and if the data can bedecoded, the decoder apparatus is activated, thereby preventing thenoise which otherwise might be caused by the decoding error of thecompressed audio data.

Japanese Unexamined Patent Publication No. 5-316056 discloses an audiosignal processing apparatus which, in order to reduce noises and clicksound, detects the number of data input of a value not contained in theconversion rule, and in the case where the detection result reaches apredetermined value or more, controls the output sound into mutedstatus.

Japanese Unexamined Patent Publication No. 8-287613 discloses an outputcontrol system of a switchable audio channel, in which in order tosuppress noises at the time of switching the audio channel, one (audiochannel 1) of a plurality of types of audio data is changed to anothertype (audio channel 2), while the audio output of audio channel 2 isfaded in after fading out the audio output of audio channel 1.

DISCLOSURE OF THE INVENTION

However, the conventional algorithm for detection of the compressedaudio data described above has the following disadvantages.

First, in the case where the DVD reproduction apparatus performs such anoperation as a trick play including what is called the double-speedreproduction for reproducing data at a speed twice as high as the normalreproduction speed, rapid feed or skip, the continuity of the datastream output from the DVD is lost. Therefore, the sync signal is lost,and in the worst case, the data may be recognized erroneously as PCMdata.

Secondly, in the rapid feed mode of the dts CD or dts LD (optical videodisk having the sound recorded therein by dts scheme) handled as normalCD, the digital data segmented regardless of the data stream are outputas PCM data. As viewed from the decoder unit, therefore, the data cannotbe discriminated from the PCM data, with the result that a noise isoutput.

Thirdly, in case of the advent of a new format with a different syncsignal specification, no protective measure is available and a noise maybe output.

The audio signal processing apparatus described in Japanese UnexaminedPatent Publication No. 5-316056 relates to the processing of audiosignal in the case where the flag cannot be detected or an error cannotbe corrected when each plurality of digital data obtained by samplingthe audio signal are transmitted with an error correcting signal, andfails to take into consideration the detection for decoding thecompressed audio data.

The output control system for a switchable audio channel described inJapanese Unexamined Patent Publication No. 8-287613 is for preventingnoises at the time of switching the audio channel in reproducing theaudio data of a plurality of channels, and also fails to take intoconsideration the detection for decoding the compressed audio data.

The present invention has been achieved in consideration of theaforementioned points, and is intended to propose an audio signalprocessing apparatus, an audio signal processing method and an opticaldisk apparatus which can suppress noises when the compressed audiodigital signal data are input.

In order to obviate this problem, in an audio signal processing methodaccording to this invention, it is detected whether the supplied datacontain consecutive zero data for a predetermined period of time, and inthe case where zero data are continued for the predetermined period oftime, it is determined that the audio data are compressed and thesupplied data are decoded.

Also, an audio signal processing apparatus according to this inventioncomprises detection means for detecting whether the supplied data hassuccessive zero data for a predetermined period of time, determinationmeans for determining that the supplied data is a compressed audio datain the case where the result of detection by the detection means showsthat zero data continue for the predetermined period of time, and decodemeans for decoding the supplied data based on the result ofdetermination by the determination means.

An audio signal processing method and an audio signal processingapparatus according to this invention have the following functions.

As long as nothing is reproduced in the optical disk apparatus, zerodata are detected as a first mode, and the stream detector in thedetection means outputs continuous zero data.

At the time of reproduction from the optical disk apparatus, a secondmode in which the input data cannot be determined prevails and theoutput is muted for a predetermined period following the time point whendata other than zero is first input to the detection means.

In the case where any sync signal is detected during the predeterminedperiod of the second mode, a decode program corresponding to the syncsignal is initiated, and the compressed digital audio data is decoded asa third mode.

In the case where a predetermined number of successive zero data aredetected during a predetermined period of time in the second mode, thecount on a counter for counting the predetermined period is cleared, andfrom that point, the second mode is maintained for a predeterminedperiod of time.

Only upon the lapse of the predetermined period of time in second modeduring which the detection is not made, the determination means judgesthat the input data is digital audio data, and immediately startsdecoding the digital audio data in the decode means as a fourth mode. Inthe process, the data for the past predetermined period of time isstored in a buffer, so that the digital audio data can be reproducedwithout interruption.

Assume, on the other hand, that the input data contains zero datacontinuously for a maximum period of time during decoding of the digitalcompressed audio data by the decode means in third mode or during thedecoding of the digital audio data by the decode means in the fourthmode. It is determined that the operation of the optical disk apparatushas stopped or the disk has been replaced, and the process proceeds tothe zero data detection mode represented by the first mode to repeat themode described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of an audio signalprocessing apparatus according to an embodiment of the presentinvention.

FIG. 2 is a diagram showing the audio data and the compressed audio dataaccording to an embodiment of the invention.

FIG. 3 is a state transition diagram of a decoder according to anembodiment of the invention.

FIG. 4 is a flowchart showing the stream detecting operation (interruptoperation) according to an embodiment of the invention.

FIG. 5 is a flowchart showing the stream detecting operation (formattedstream block) according to an embodiment of the invention.

FIG. 6 is a flowchart showing the stream detecting operation (streamcheck block) according to an embodiment of the invention.

FIG. 7 is a flowchart showing the stream detecting operation(unformatted stream block) according to an embodiment of the invention.

FIG. 8 is a flowchart showing the stream detecting operation (PCM checkblock) according to an embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An audio signal processing apparatus according to an embodiment of theinvention will be described in detail below with reference to thedrawings appropriately.

FIG. 1 is a block diagram showing a configuration of an audio signalprocessing apparatus of an optical disk reproduction apparatus accordingto an embodiment of the invention.

The audio signal processing apparatus according to the invention shownin FIG. 1 is for outputting the audio signal by decoding the digitalaudio signal. In order to suppress the noise when the compressed audiodigital data are input, this apparatus detects the continuous zero datafor several samples constituting the feature of the compressed audiodata, suspends the audio decoding when a signal or data other than thedigital signal of PCM type, i.e. the digital audio signal notcompressed, decodes the compressed data and mutes the audio output.

The signal read by the optical pickup from the DVD as a disk-shapedrecording medium is converted into an electrical signal and amplified inan optical disk reproduction unit, and the analog signal is convertedinto a digital signal by an A/D converter and supplied to a signalprocessing circuit. In the signal processing circuit, the signal readfrom the DVD is demodulated, the error corrected, and the processperformed for demodulation against the 8/16 modulation, therebyoutputting an audio stream. This audio stream is supplied to an audiosignal processing apparatus making up a decode unit shown in FIG. 1.This audio stream contains the audio data compressed or not compressedin the format of AC-3, MPEG or dts, i.e. PCM digital audio data.

The PCM digital data is a non-compressed digital audio data of 48 kHz or96 kHz in sampling frequency. AC-3 is a compression scheme used for SR-D(Dolby Stereo Digital, trade mark). MPEG (Moving Picture Experts Group)is defined up to the MPEG2 expansion bit stream to handle amulti-channel. The compression scheme dts (digital theater systems,trade mark) corresponds to the digital multi-tracks.

In FIG. 1, the compressed audio data of AC-3 format reproduced from theDVD, for example, is supplied to the RF circuit 1 of AC-3 forhigh-frequency wave amplification, shaped in a BPF (bandpass filter)waveform shaping circuit 4, high-frequency modulated in a RF demodulator5 and a high-speed SRAM 6, and supplied to a switch (SW) 7. Thecompressed audio data in dts format or MPEG and the PCM digital audiodata are supplied to a switch (SW) 7 through optical signal inputcircuits OP1 (2-1), OP2 (2-2) and . . . . The signal supplied from theRF demodulator 5 and each optical signal input circuit through theswitch (SW) 7 is supplied to a recording output circuit (REC OUT) 3 andrecorded, for example, in the optical disks of an optical diskrecording/reproduction apparatus.

In this way, the digital audio signal reproduced from the DVD isselected by the switch (SW) 7 and demodulated as an audio sample in adigital interface receiver 8. This demodulated signal is supplied to adecoder 9. The decoder 9 is configured with a DSP (digital signalprocessor), which after detection of a stream as described later,expands and decodes the compressed audio data of AC-3, MPEG or dtsformat, while at the same time decoding the PCM digital data. The audiocompression in the encode operation is elimination of the redundantportion due to the masking effect, and therefore the decoding of thecompressed audio data is a process for restoring the compressed data tothe original form.

The two-channel audio signal decoded by the decoder 9 is converted intodigital audio signals of six channels including L (left), R (right), C(center), SW (subsidiary low), SL (subsidiary left) and SR (subsidiaryright) by a multi-channel decoder 10 and a high-speed SRAM 11. Thesix-channel audio signals of L, R, C, SW, SL and SR have the jitterthereof removed by jitter removing circuits 12-1, 12-2, 12-3,respectively, and converted into six-channel analog audio signals of L,R, C, SW, SL, SR using the clock from a crystal oscillation circuit(OSC) 14 by D/A conversion circuits 13-1, 13-2, 13-3, respectively.

The six-channel analog audio signals of L, R, C, SW, SL and SR areconverted into the magnitude of output current corresponding to the8-bit serial signal by current D/A conversion circuits 15-1, 15-2, 15-3,15-4, 15-5, 15-6, respectively, and a reference signal 16, and convertedfrom current to voltage by I (current)/V (voltage) conversion and LPFs(low pass filters) 16-1, 16-2, 16-3, 16-4, 16-5, 16-6, have the signalin the audio area retrieved, amplified in amplifiers 17-1, 17-2, 17-3,17-4, 17-5, 17-6, have the outputs thereof suspended by muting switches18-1, 18-2, 18-3, 18-4, 18-5, 18-6 including relays and a relay drivecircuit 20 while the data are decoded by the decoder 9, and outputthrough an output switching circuit 21 including a relay. The operationof each of the circuits described above is controlled by a controller22.

FIGS. 2A and 2B are diagrams showing the audio data and the compressedaudio data according to this embodiment.

The audio PCM data 23 shown in FIG. 2A is basically the result ofsampling the sound existing in the natural world, and therefore veryrarely continues to be zero for a certain period of time. Even if acontinuously zero data exists, the probability of the pattern beingrepeated over a predetermined period of time is substantially zeroexcept for the muted state lacking the sound.

The compressed audio data 25, 28 shown in FIG. 2B basically exist inbursts with burst preambles 24, 27, and have the feature of being alwaysaccompanied by a certain period of time during which the zero data 26exists. In the IEC61937 format which is a digital audio specification ofDVD, the sync signal itself has 4-sample zero data, and therefore thereis always a period during which continuous zero data 26 of at least 4samples appear.

According to this embodiment, not only the conventional sync signal butalso the continuous zeros constituting the feature of the compressedaudio data based on the IEC61937 format is detected as a criterion forthe compressed audio data in the decoder 9 thereby to detect the streamof the compressed audio data.

FIG. 3 is a state transition diagram of the decoder 9 according to thisembodiment.

In FIG. 3, in the case where nothing is reproduced in the optical diskreproduction apparatus, as shown in state 1 (30), the zero datadetection state basically prevails, so that the continuous zero data isoutput from the stream detector of the decoder 9.

In the case where the DVD is reproduced in the optical disk reproductionapparatus from this state 1 (30), as indicated first by referencenumeral 31, the UNKNOWN state prevails in which the input data cannot bedetermined as indicated by state 2 (32) during the 1024 sample periodsafter the time point when the data other than zero is input to thedecoder 9, and the output remains muted by the muting switch 19.

In the case where some sync signal is detected as indicated by referencenumeral 33 during the 1024 sample periods in the UNKNOWN state as shownin state 2 (32), the decode program corresponding to the detected syncsignal is started. Thus, as shown in state 3 (34), the compressed audiodata is decoded based on AC-3, MPEG, dts, etc. Also, when the decodeprocess is started, the muted state by the muting switch 19 is canceled,and the audio signal based on the output data from the decoder 9 isoutput. The canceling operation or the muting operation of the mutingswitch 1 is controlled by the controller 22 described above.

If three samples of continuous zero data are detected as indicated byreference numeral 36 during the 1024 sample periods of the UNKNOWN stateindicated by state 2 (32), the count of the counter for counting the1024 samples is cleared as indicated by reference numeral 37, andfurther the UNKNOWN state for 1024 samples is maintained from thatpoint.

Only at the time point when the sync signal is not detected during the1024 sample periods from the UNKNOWN state indicated by state 2 (32) asdesignated by reference numeral 38, it is determined that the input datais the PCM data and, as indicated by state 4 (39), the PCM dataimmediately begins to be decoded. In the process, the data for the past1024 samples are stored in the buffer memory in the decoder 9, so thatthe audio data of PCM scheme can be reproduced without interruption. Themuted state of the muting switch 19 is canceled and the audio signal isoutput based on the data output from the decoder 9.

In the case where the input data indicated by reference numeral 35 or 41remains zero data for a long time, say, one second during the decodingof the audio data compressed by AC-3, MPEG or dts scheme indicated bystate 3 (34) or during the decoding of PCM data indicated by state 4(39), then it is determined that the operation of the optical diskreproduction apparatus has stopped or the disk has been replaced, andthe process is transferred to the zero data detection state shown in thefirst state 1 (30). This state transfer is repeated. In the process, themuting switch 19 is switched to muting mode.

FIGS. 4 to 8 are flowcharts showing the operation of stream detection ofthe decoder 9 according to this embodiment. These flowcharts show thedetailed operation of the stream detection unit of the decoder 9.

In FIG. 4, assume that the signal reproduced from the DVD is supplied tothe decoder 9 through the switch (SW) 7, for example, and the interruptoperation is started. At step S1, the sample data are fetched, and 64samples are counted at step S2. At step S3, it is determined whether thecompressed audio data stream is involved or not based on the IEC61937format described above, for example. In the case where the digital datasupplied at step S3, i.e. the data stream is compressed in audio form,the process proceeds to step S4 for determining whether the formatstream is involved or not. In the case where it is determined that noformatted stream is involved at step S4, the process proceeds to theunformatted stream block S5, while in the case where the formattedstream is involved, the process proceeds to the formatted stream blockS6 and returns.

In the case where the data stream of the compressed audio data is notinvolved at step S3, the process proceeds to step S7 for determiningwhether the data can be fetched or not. In the case where the data canbe fetched, the process proceeds to step S8 for determining whether theXPCM (the channel status of the data stream is not PCM data) flag is setor not. In the case where the channel status is not PCM data at step S8,the process proceeds to step S9 for determining whether the ForcePCM(PCM data is most likely to be involved) flag is set or not. In the casewhere the PCM data is most unlikely to be involved, the process proceedsto step S10 for determining whether the PCM detection flag is set ornot. In the case where it is detected that the PCM detection flag is notset at step S10, the process proceeds to step S11 for determiningwhether the auxiliary MaybePCM (probable PCM) flag is set or not. In thecase where it is detected at step S11 that the PCM flag is probably set,the process proceeds to step S12, so that the process for transfer ofthe PCM data to the process of the subsequent stages is performed in thePCM block.

In the case where the probability of being PCM data is high at step S9,or when it is detected at step S10 that the PCM detection flag is set,the process proceeds to step S12, and the process for transfer of thePCM data is performed in the PCM block. In the case where it is notprobably the PCM data at step S11, the process proceeds to step S13 andthe process of the stream check block is performed. In the case wherethe data cannot be fetched at step S7 or in the case where the channelstatus is not PCM data at step S8, the process proceeds to step S13where the process of the stream check block shown in FIG. 6 is performedfollowed by returning.

FIG. 5 shows a subroutine of the format stream block of step S6 shown inFIG. 4. The formatted stream block in FIG. 5 is the process performed inthe case where the input data is the audio data compressed by the AC-3,dts or MPEG scheme and the decoder 9 is decoding the audio dataaccording to AC-3, dts or MPEG scheme.

In FIG. 5, when the formatted stream block is started, it is determinedat step S20 whether the stream block count ==0 (whether 0s are countedcontinuously) or not. In the case where the 0s are counted continuously,the process proceeds to step S21, and the burst preamble Pc for thepreceding sampling is set to −1. At step S22, the value of each flag inthe initialization block is initialized to 0 for stream detection, 0 forthe formatted stream, UNKNOWN for the message, 0 for the burst syncdetection, 0 for required transfer, 0 for MaybePCM, 0 for MaybeDTS,PCMMAX for PCM count and PCMZEROMAX for PCM zero. In the process, theUNKNOWN state shown in state 2 (32) of FIG. 3 prevails. Then the processproceeds to the stream check block shown in FIG. 6. Step S20 correspondsto the zero data detection of state 1 (3) shown in FIG. 3.

In the case where the stream block count value is not continuous 0s atstep S20, the process proceeds to step S23 for stream count −−(decrement). At step S24, it is determined whether the transfer isrequired or not, and if the transfer is required, the process proceedsto step S25 and Temp is set to {Pd (indicating the frame length of theburst preamble)—sample count} as a provisional value. Further, theprocess proceeds to step S26 for determining whether Temp>0 or not. Inthe case where Temp>0 at step S26, the transfer count is set to thesample count at step S27, Pd is set to Temp at step S28, and the processproceeds to step S31 for processing the transfer data block. Unless Tempis larger than 0 at step S26, the transfer count is set to Pd at stepS29 and the required transfer is set to 0 (cleared) at step S30. Thenthe process proceeds to step S31 for processing the transfer data block.Step S31 indicates the state in which the compressed audio data of state3 (34) shown in FIG. 3 is being decoded or the PCM data of state 4 (39)is being decoded.

At step S32, the sample count is set to the transfer count less thesample count, and the process proceeds to step S33 for determiningwhether the sample count is larger than 0 or not. If the sample count islarger than 0 at step S33, the process proceeds to step S37 describedlater, while when the sample count is not larger than 0, the process isreturned.

Unless the transfer is required at step S24, the process proceeds tostep S34 for determining whether the burst sync is detected or not.Steps S34 to S47 represent the sync detection 40 or the sync detection33 shown in FIG. 3. In the case where the burst sync is detected at stepS34, the process proceeds to step S35 for setting the burst syncdetection to 0 (clear). Unless the burst sync is detected at step S34,on the other hand, the process proceeds to step S36 for determiningwhether the sample count == 0 (whether continuous 0s are counted) ornot. If the sample count == 0, i.e. 0s are counted continuously, theprocess is returned. Unless the sample count == 0, i.e. if continuous 0sare not counted at step S36, the process is advanced by one sample atstep S37, followed by step S38 where the sample count −− is made(decremented). Then, at step S39, it is determined whether the sample ==IEC signal (IEC61937 format) or not. In the case where the sample == IECsignal at step S39, the process proceeds to step S40 for determiningwhether the sample count == 0 (continuous 0s) or not, and if the samplecount == 0 (continuous 0s), the process proceeds to step S41. The burstsync detection is set to 1 and the process is returned, while unless thesample count == 0 or the burst sync detection is set to 0 (cleared) atstep S35, the process proceeds to step S42.

At step S42, the process is advanced by one sample, followed by step S43for sample count −− (decrement). At step S44, it is determined whetherthe previous Pc=Pc or not, and if the previous Pc equals Pc, the processproceeds to step S45 for determining whether Pd ==0 or not. Unless theprevious Pc = Pc, the process proceeds to step S53, and setting theprevious Pc equal to Pc, the process proceeds to the processing block ofstep S22. Also when Pd== 0 at step S45, the process proceeds to theprocessing block at step S22. The process of steps S20 to S53corresponds to the data input other than zero indicated by referencenumeral 31 in FIG. 3.

Unless Pd== 0 (continuous 0s) indicating the frame length at step S45,the value of each flag is set to 1 for stream detection, 0 for PCMdetection and 0 for MaybePCM at step S46, and the process proceeds tostep S47. It is determined at step S47 whether Pc indicating the syncpattern of the burst preamble is 1, 4, 5, 6, 8, 9, 11, 12, 13, and ifPc=1, 4, 5, 6, 8, 9, 11, 12, 13, the process proceeds to step S48 wherethe message is set to AC-3, dts or MPEG, followed by step S49 forsetting the required transfer to 1. Then, at step S50, the stream countis set to MAX for transfer of AC-3, dts and MPEG, followed by returningto step S20. In the process, the compressed audio data of state 3 (34)shown in FIG. 3 is being decoded. Unless Pc is 1, 4, 5, 6, 8, 9, 11, 12,13 at step S47, the process proceeds to step S51 where the message isset to UNKNOWN, followed by step S52 for setting the stream count at 0.5sec/64, and then the process is returned to step S20. In the process,the UNKNOWN mode of state 2 (32) shown in FIG. 3 prevails.

FIG. 6 shows a subroutine of the stream check block at step S13 in FIG.4. The stream check block of FIG. 6 is the process performed in the casewhere the input signal is the PCM data and the PCM data is being decodedor in UNKNOWN mode.

In FIG. 6, once the stream check block is started, it is determined atstep S60 whether the sample count == 0 (continuous 0s), and if thesample count == 0, the process is returned, all while unless the samplecount == 0, the process proceeds to step S61 for determining whether theburst sync has been detected or not. If the burst sync is detected atstep S61, the process proceeds to step S62 where the burst syncdetection is set to 0 (clear), followed by step S62 for leading onesample, the sample count is set to −− (decremented) at step S64, and itis determined whether the previous Pc == Pc or not at step S65. In thecase where the previous Pc == Pc at step S65, the process proceeds tostep S66, and the formatted stream is set to 1, followed by proceedingto step S45 of the formatted stream block in FIG. 5 described above,through (f). Unless the previous Pc == Pc at step S65, on the otherhand, the process proceeds to step S67 for setting the previous Pc to Pcand the process returns to step S60.

Unless the burst sync is detected at step S61, the process proceeds tostep S68, and leading by one sample, the sample count is set to −−(decremented) at step S69, and it is determined at step S70 whetherMaybeDTS prevails or not. In the case where Maybe dts is involved atstep S70, the DTS sample count is incremented (++) at step S71, while inthe case where Maybe dts is not involved in step S70, the processproceeds directly to step S72 for determining whether the sample is theIEC signal (IEC61937 format) or not. In the case where the sample is theIEC signal at step S72, the PCM count is set to PCMMAX at step S73, andit is determined at step S74 whether the sample count ==0 or not. In thecase where the sample count == 0, the burst sync detection is set to 1at step S75, followed by returning the process. Unless the sample count== 0 at step S74, on the other hand, the process proceeds to step S62described above.

In the case where the sample is not the IEC signal at step S72, theprocess proceeds to step S76 for determining whether the sample == DTSsync or not. In the case where the sample == DTS sync at step S76, thePCM count is set to PCMMAX at step S77, followed by step S78 fordetermining whether MaybeDTS is involved or not. In the case whereMaybeDTS is involved at step S78, the process proceeds to step S79 fordetermining whether the dts sample count == 512, 1024, 2048 or 4096 ornot. This operation is performed by determining whether the headerappears at the same period as dts during the decoding of the data.

In the case where the DTS sample count == 512, 1024, 2048, 4096 at stepS79, the previous Pc is equal to −1 at step S80, and the message isequal to DTS at step S81. Then, at step S82, the values of the flags areset to 1 for stream detection, 0 for PCM detection, 0 for MaybePCM, 0for formatted stream, 64 less the sample count for offset, 64, 32, 16 or8 for TDSCOUNTMAX, and DTSCOUNTMAX for DTS count. At step S83, the DTSsync is copied to the buffer memory of the decoder 9 for transfer. Thisindicates that the compressed audio data in state 3 (34) of FIG. 3 isbeing decoded. At step S84, it is determined whether the sample count ==0 (continuous 0s) or not, and if the sample count == 0, the process isreturned, while unless the sample count == 0, the process proceeds tostep S92 of the unformatted stream block of FIG. 7 described laterthrough (g).

Unless the DTS sample count == 512, 1024, 2048 or 4096 at step S79, theDTS sample count is set to 0 at step S85, and the process returns tostep S60.

In the case where MaybeDTS is not involved at step S78, the processproceeds to step S86 for setting the DTS sample count to 0 and MaybeDTSto 1, followed by returning to step S60.

Unless the sample == DTS sync at step S76, the process proceeds to thePCM check block at step S87 for performing the PCM detection asdescribed later and the process is returned to step S60.

FIG. 7 shows a subroutine of the unformatted stream block of step S5 inFIG. 4. The unformatted stream block in FIG. 7 is the process performedin the case where the input signal is not based on the DVDspecification.

In FIG. 7, once the unformatted stream block is started, the DTS countis decremented (−−) at step S90, the sample count is set to 64 at stepS91, and the sample count data is copied to the buffer for dataretrieval at step S92.

At step S93, it is determined whether the DTS count ==0 (continuous 0s)or not, and in the case where the DTS count == 0 0, the DTS sync of thebuffer is checked at step S94 thereby to check whether the DTS sync islocated at the specified position or not. Upon detection of the sync atstep S95, the DTS count is set to TDSCOUNTMAX at step S96 so that thestream is detected, followed by returning the process. In the case whereno sync is detected at step S95, the process proceeds to the streamcheck block shown in FIG. 6. Unless the DTS count == 0 at step S93, theprocess is returned.

FIG. 8 shows a PCM check subroutine of step S87 of the stream checkblock shown in FIG. 6. FIG. 8 shows the process performed in the UNKNOWNmode.

In FIG. 8, once the PCM check block is started, it is determined at stepS100 whether one sample == 0 (continuous *0s) or not. If one sample ==0, the process proceeds to step S101, the PCM zero is decremented (−−)and it is determined at step S102 whether the PCM zero <=(PCMZEROMAX−3).In the case where the PCM zero <=(PCMZEROMAX−3) at step S102, on theother hand, the PCM count is set to PCMMAX at step S103, and the processproceeds to step S104. Unless the PCM zero <=(PCMZEROMAX−3) at stepS102, on the other hand, the process directly proceeds to step S104.Step S102 corresponds to the zero detection for three samples in rowindicated by reference numeral 36 in FIG. 3, and step S103 correspondsto the counter clear designated by 37 in FIG. 3. At step S104, it isdetermined whether PCM zero == 0 (continuous 0s) or not, and if PCM zero== 0, the process proceeds to step S105, and the message is set to PCMzero, so that PCM zero=PCMZEROMAX at step S106. At step S107, the PCMdetection is set to 0, and MaybePCM to 0, followed by step S108 forsetting the PCM count to PCMMAX and the previous Pc to −1 thereby toterminate the PCM check block zero. Unless the PCM zero == 0 at stepS104, the PCM check block is directly terminated.

Unless one sample == 0 (continuous 0s) at step S100, the processproceeds to step S109 and the PCM count is decremented (−−) so that thePCM is set to PCMZEROMAX at step S110. At step S111, it is determinedwhether the PCM count == 0 or not. If the PCM count == 0, the processproceeds to step S112, and the message is set to PCM, followed by stepS113 for setting the PCM detection to 1. Then the process proceeds tostep S108 described above. Steps S115 and S116 correspond to the casewhere counter>1024 (PCM detection) as designated by reference numeral 38in FIG. 3. Steps S109 and S111 correspond to the continuous zero datadetection for one second indicated by reference numeral 35 or 41 in FIG.3.

Unless the PCM count == 0 at step S111, the process proceeds to stepS114 for determining whether the PCM is detected or not. In the casewhere the PCM is detected at step S114, the PCM check block is endeddirectly. If the PCM is not detected, on the other hand, the processproceeds to step S115 for determining whether PCM count>(PCMMAX−1024) ornot. In the case where PCM count>(PCMMAX−1024) at step S115, the processproceeds to step S117 where the message is set to UNKNOWN and the PCMcheck block is ended. Unless PCM count>(PCMMAX−1024) at step S115, theprocess proceeds to step S116 and after setting MaybePCM to 1, proceedsto step S117.

An audio signal processing apparatus for decoding the input digitalaudio data and outputting an audio signal according to this embodimentcomprises a decoder 9 for determining that the input signal is thedigital data stream of a compressed sound upon detection of zero datawhich continues for at least a predetermined length of time, wherein thedigital data stream is decoded by the decoder 9 and the audio signal isoutput. Thus, even in the case where the trick play (what is calleddouble-speed reproduction, rapid feed or skip) is performed in theoptical disk reproduction apparatus supplied with the input signal orotherwise the continuity of the input data stream is lost, the inputsignal is not erroneously recognized as digital audio data (PCM), andtherefore noises can be prevented.

According to the embodiment described above, the optical disk can be arecordable one other than the DVD.

In the audio signal processing method according to the invention, it isdetermined whether the zero data continues in the supplied data for apredetermined length of time or not, and in the case where the zero datacontinues for the predetermined length of time, it is determined thatthe audio data is involved, and the supplied data are decoded.Therefore, even in the case where the trick play (what is calleddouble-speed reproduction, rapid feed or skip) is performed in theoptical disk reproduction apparatus (DVD player) supplied with the inputsignal or otherwise the continuity of the input data stream is lost, theinput signal is not erroneously recognized as digital audio data (PCM),and therefore noises can be prevented.

In the audio signal processing method according to this inventiondescribed above, upon detection of the continuous zero data for thepredetermined period of time, the data supplied is switched to thedecode operation based on the sync signal for the supplied data. Even inthe case where an input signal of new format having a different syncsignal specification appears, therefore, it is determined that the inputsignal is the compressed audio digital data as long as the continuouszero data exceeding the predetermined period of time exists in thecompressed audio data. Thus, the erroneous recognition of the inputsignal as digital audio data (PCM) is prevented, thereby making itpossible to prevent the noises.

Also, with the audio signal processing method according to the inventiondescribed above, in the case where the continuous zero data for thepredetermined period of time are not detected, it is determined that thenon-compressed audio data is involved and the decode operation isperformed. Therefore, the PCM detection can be carried out withoutresorting to the PCM flag unlike in the prior art. Also, even in thecase where the digital data interrupted randomly regardless of thestream are output as PCM data in such an operation as rapid feed of theoptical disk having the audio data recorded therein according to the dtsscheme handled as the normal CD, it is determined from the detection ofcontinuous zero data that the compressed audio data are involved. Inthis way, at least it is determined that the PCM is not involved,thereby making it possible to prevent noises.

Also, in the audio signal processing method according to this inventiondescribed above, the supplied audio data are stored for thepredetermined period during the detection whether the zero data arecontinuously detected or not, and in the case where it is determinedthat the non-compressed audio data prevails, the result of decoding thesupplied data is output following the result of decoding the storedaudio data is output. Without discontinuation of the output data,therefore, the audio data of PCM scheme can be reproduced.

Further, in the audio signal processing method according to thisinvention described above, the output of the decoded data is muted forthe predetermined period of time during which it is detected whether thecontinuous zero data exist or not. Therefore, the noises can beprevented by muting the output while the determination on the input datais impossible.

Furthermore, with the audio signal processing method according to theinvention described above, in the case where the data supplied duringthe decode operation is the continuous zero data, the detect operationis performed again for determining whether the zero data continues forthe predetermined period of time. Therefore, the state in which nothingis reproduced in the optical disk reproduction apparatus is detected andnoises can be prevented.

Also, the audio signal processing apparatus according to this inventiondescribed above comprises detection means for detecting whether thesupplied data contain continuous zeros for a predetermined period oftime, and determining means for determining that the supplied data isthe compressed audio data in the case where the detection result of thedetection means indicates that the continuous zero data exist for thepredetermined period of time, and decode means for decoding the supplieddata based on the result of determination by the determining means. Inthe case where the trick play (double-speed reproduction, rapid feed orskip) is performed in the optical disk reproduction apparatus (DVDplayer) for supplying the input signal or otherwise in the case wherethe input data stream comes to lose the continuity, the erroneousrecognition that the input signal is the digital audio data (PCM) iseliminated, thereby making it possible to prevent noises.

Also, with the audio signal processing apparatus according to theinvention described above, upon detection by the detection means thatthe continuous zero data exist for the predetermined period of time, thedecode operation is switched based on the sync signal of the supplieddata, and the supplied data are decoded. Even in the case where an inputsignal of new format appears with a different sync signal specification,it is determined that the input signal is the compressed audio digitaldata as long as the continuous zero data exists for a time longer than apredetermined period of time in the digital compressed audio data. Thus,the erroneous recognition that the input signal is the digital audiodata (PCM) can be prevented.

Further, with the audio signal processing apparatus according to theinvention described above, in the case where the continuous zero dataare not detected during the predetermined period of time, thedetermining means determines that the non-compressed audio data areinvolved. Therefore, the PCM detection can be performed withoutresorting to the PCM flag unlike in the prior art. Also, even in thecase where digital data randomly interrupted without regard to thestream are output as PCM data during the rapid feed of the optical diskhaving recorded therein audio data according to the dts scheme handledas a normal CD, it is determined that the compressed audio data isinvolved based on the detection of the continuous zero data. Bydetermining at least that the PCM is not involved, therefore, noises areprevented.

Also, with the audio signal processing apparatus according to theinvention described above, the decode means includes a memory forstoring the audio data supplied for the predetermined period of timeduring which it is detected whether the continuous zero data aredetected or not. Upon determination that the non-compressed audio dataare involved, the apparatus outputs the data decoded from the supplieddata as the continuous output decoded by the decode means from the audiodata stored in the memory. Therefore, by storing the data correspondingto the past samples for the predetermined period of time, the audio dataof PCM scheme can be reproduced without interruption of the output data.

Further, the audio signal processing apparatus according to theinvention described above comprises muting means for muting the outputof the data decoded for the predetermined period of time during which itis determined whether the continuous zero data are detected, andtherefore the output with the input data impossible to determine ismuted thereby to prevent noises.

Also, with the audio signal processing apparatus according to theinvention described above, the muting means cancels the muting operationwith the start of the decode operation by the decode means. Therefore,the smooth audio output can be started with the decode operation startedbased on the input data determination, thereby preventing noises.

Further, with the audio signal processing apparatus according to theinvention described above, in the case where the data supplied duringthe decode operation by the decode means is the continuous zero data,the detection means again detects the data supplied. Therefore, thestate in which nothing is reproduced in the optical disk reproductionapparatus is continuously detected, thereby preventing noises.

The apparatus is used for the decode operation for suppressing thenoises of the audio data supplied to the decoder unit from an opticaldisk apparatus outputting the audio signal read by an optical pickupfrom a disk (DVD).

1. An audio data signal processing method, in which a supplied audiodata signal can be in one of a compressed data state and an uncompresseddata state, for performing a process for decoding the supplied audiodata signal, comprising the steps of: detecting whether zero datacontinues for a predetermined period of time in said supplied audio datasignal; determining, when zero data are detected to continue for saidpredetermined period of time, that said supplied audio data are in thecompressed data state and determining, when zero data is not detected tocontinue for said predetermined period of time, that said supplied audiodata are in the uncompressed state; performing a first decodingoperation on said supplied audio data when said supplied audio data aredetermined to be in the compressed data state in said step ofdetermining; and performing a second decoding operation on said suppliedaudio data when said supplied audio data are determined to be in theuncompressed data state in said step of determining, wherein upondetection that zero data continue for said predetermined period of time,said decoding is performed by automatically switching said suppliedaudio data signal to said first decoding operation based on a syncsignal of said supplied audio data signal, and wherein said suppliedaudio data are stored for said predetermined period during which it isdetected whether said zero data continue.
 2. The audio signal processingmethod described in claim 1, wherein the output of said decodingoperation is muted for said predetermined period of time during which itis detected whether zero data continue for said predetermined period oftime.
 3. The audio signal processing method described in claim 1,wherein when said data supplied during said decode operation arecontinuous zero data, the operation for detecting whether said zero datacontinue for said predetermined period of time is repeated.
 4. An audiosignal processing apparatus comprising: detection means for detectingwhether zero data continue for a predetermined period of time insupplied audio data; determining means for determining that saidsupplied audio data is compressed audio data when a result of detectionby said detection means is that zero data continues for saidpredetermined period of time; and decoding means for decoding saidsupplied audio data based on the result of said determination by saiddetermining means, wherein when said detection means detects that zerodata continue for said predetermined period of time, said decoding meansswitches to a first decoding based on a sync signal of said supplieddata and decodes said supplied audio data, and wherein said determiningmeans determines that said supplied audio data are uncompressed audiodata when zero data are not detected continuously for said predeterminedperiod of time and said decoding means automatically switches to asecond decoding and decodes said supplied audio data, wherein saiddecoding means includes a memory for storing said supplied audio datafor said predetermined period of time during which it is determinedwhether zero data are continuously detected.